The 2012–13 Top League was the tenth season of Japan's domestic rugby union competition, the Top League. It kicked off on 31 August 2012. The final was held on 27 January 2013 and won by Suntory Sungoliath to claim their third Top League title.

Japan Rugby League One is a rugby union competition in Japan. It is the highest level of professional rugby competition in the country. The Japan Rugby Football Union created the competition in 2003, by absorbing the Japan Company Rugby Football Championship, to drive up the overall standard and popularity of the sport and improve the results of the Japan national rugby union team. The chief architect of the league was Hiroaki Shukuzawa who strongly felt the urgency of improving Japanese domestic company rugby to a professional level which would allow Japan to compete more convincingly at Rugby World Cups.